GetHeight x y is the function for getting the specific height of the specific position which will make you be able to walk on the terrain instead of going right through.
Check out this thread to see it in action: http://www.alice.org/community/showthread.php?t=4102

Hey Zenteo, if I was in charge of A-TOM then you wouldn't need a job interview. Never really seen anything from you before until I noticed your terrain pack on the A-TOM website, then up here you popped. I like the terrain pack a lot.